ACS at the Atacama Pathfinder
Experiment (APEX)
Dirk Muders
Max-Planck-Institut
für Radioastronomie
Bonn
ACS Workshop, ESO Garching, 03/2004
The APEX Project
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APEX is a 12m radio telescope located
north of the ALMA site on Chajnantor at
5100m
APEX is a pathfinder mission aimed at
exploring the southern sub-mm sky in
preparation for ALMA
APEX is a collaboration between MPIfR,
AIRUB, ESO and OSO
ACS Workshop, ESO Garching, 03/2004
The APEX Project (cont.)
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APEX is a copy of the US ALMA prototype
antenna built by VERTEX
Compared to the ALMA telescope APEX
features two additional Nasmyth receiver
cabins, an instrument container and a
compressor platform
ACS Workshop, ESO Garching, 03/2004
APEX Interfaces
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APEX uses the same vendor-supplied
control computers (ACU & PTC) and the
same CAN bus interface (ICD 9) like
ALMA
It was thus decided to re-use the ALMA
prototype telescope control software
(TICS) and most of the corresponding
control hardware setup
ACS Workshop, ESO Garching, 03/2004
APEX Instrumentation
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The APEX instrumentation will consist of:
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Bolometer cameras with several hundred
pixels (e.g. LABOCA) at λ=1 mm to 350 μm
Heterodyne receivers (single-pixel and arrays)
at ν=230 GHz to 1.5 THz (200 μm)
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Continuum backends
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Auto-Correlators
ACS Workshop, ESO Garching, 03/2004
APEX Status
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APEX has been erected in early 2003
In September 2003 the telescope control
system hard- and software were installed
Preliminary acceptance tests took place in
November 2003
Currently the pointing is being checked
with an optical telescope
ACS Workshop, ESO Garching, 03/2004
ACS Workshop, ESO Garching, 03/2004
Difficulties at 5000m:
Low pressure
Low oxygen content
Oxygenization
Pressurized Hard
DriveBox
ACS Workshop, ESO Garching, 03/2004
ACS / TICS at APEX
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APEX is using TICS and thus ACS
The ACS version in use is determined by
TICS (currently ACS 2.0.1)
We will probably upgrade to ACS 3.0.1 this
year if a new (stable) TICS port will be
available
ACS Workshop, ESO Garching, 03/2004
ACS / TICS at APEX (cont.)
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TICS provides antenna control
(astronomical coordinate tracking,
patterns, CAN bus access, etc.) via 4 COBs
ALMA's timing setup is much more
complicated than needed for APEX
APEX uses GPS & IRIG-B to slave the
ABM to TAI and a hardware timing
generator for the 48ms Timing Events
ACS Workshop, ESO Garching, 03/2004
APEX Instrument Interfaces
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APEX instrumentation needs to be
interfaced to the ACS -> make components
Many instruments are legacy devices that
use a simple ASCII protocol over a socket
rather than the CAN bus that ALMA
employs
Thus a socket DevIO implementation is
needed
ACS Workshop, ESO Garching, 03/2004
APEX Socket DevIO
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The socket code needs to handle sending
and parsing ASCII messages for
component properties AND for methods
It must handle multiplexing and
concurrent accesses to the component
properties
The messages are standardized using the
SCPI syntax
ACS Workshop, ESO Garching, 03/2004
Socket DevIO Class Diagram
ACS Workshop, ESO Garching, 03/2004
SCPI Syntax
Component sends the device:
[APEX:]<device name>:<property/method name>?
The device replies:
[APEX:]<device name>:<property/method name> <value> \
<ISO 8601 time stamp>
Example:
APEX:SIS345:LO2:MULTI1:backShort2?
APEX:SIS345:LO2:MULTI1:backShort2 2.341 \
2003-11-05T10:19:38.310+00.00
ACS Workshop, ESO Garching, 03/2004
APEX Instruments IDLs
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The instrument IDLs are kept as generic as
possible to be able to re-use them for new
instruments of the same kind; only a new
CDB entry is needed
Instruments are implemented via a
hierarchical device tree to:
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have one high-level interface for observing
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have low-level interface(s) for engineering
ACS Workshop, ESO Garching, 03/2004
APEX Device Hierarchy
APEX:SIS345
APEX:SIS345:CALUNIT
APEX:SIS345:MIXER1
APEX:SIS345:MIXER1:COLDAMP
APEX:SIS345:MIXER2
APEX:SIS345:MIXER2:COLDAMP
APEX:SIS345:LO1
APEX:SIS345:LO1:GUNN
APEX:SIS345:LO1:PLL
APEX:SIS345:LO1:MULTI1
APEX:SIS345:LO1:MULTI2
APEX:SIS345:LO2
APEX:SIS345:LO2:GUNN
APEX:SIS345:LO2:PLL
APEX:SIS345:LO2:MULTI1
APEX:SIS345:LO2:MULTI2
apexHFE.idl
apexHFE_HCal.idl
apexHFE_Mixer.idl
apexHFE_ColdAmp.idl
apexHFE_Mixer.idl
apexHFE_ColdAmp.idl
apexHFE_LO.idl
apexHFE_Gunn.idl
apexHFE_PLL.idl
apexHFE_Multi.idl
apexHFE_Multi.idl
apexHFE_LO.idl
apexHFE_Gunn.idl
apexHFE_PLL.idl
apexHFE_Multi.idl
apexHFE_Multi.idl
ACS Workshop, ESO Garching, 03/2004
Code generation
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The C++ component code is automatically
generated from the IDLs using a modified
version of the “bdsGenerator” from AIRUB
C++, *.h, xml and xsd files are created
DevIOUDPSock socket communication code
& SCPI commands are automatically added
Embedded system host name and port are
stored in the CDB and read at startup
ACS Workshop, ESO Garching, 03/2004
Serial & GPIB Devices
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Many commercial devices use RS232 or
GPIB communication with given commands
General problem of non-concurrent access
-> need to serialize commands
Demultiplexing is done in the standalone
SCPI command parser (CID) which in turn
talks to the hardware, i.e. CID is a “driver”
Socket DevIO is re-used here
ACS Workshop, ESO Garching, 03/2004
CID Setup
ACS Workshop, ESO Garching, 03/2004
Device Emulators
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A simple Python script was developed to
emulate socket devices
The emulator uses the IDLs and sets up all
property types automatically
Simple funtionality such as setting actual
to commanded values is included
Can be extended easily
ACS Workshop, ESO Garching, 03/2004
APEX Control System (APECS)
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For real observations all those components
need to be set up and coordinated to
perform “scans”. This is done by the
“APEX Observing Engine”
The APEX raw data format (MBFITS) was
defined based on ALMA's TI-FITS
The raw data writer collects telescope and
backend data to write MBFITS files
ACS Workshop, ESO Garching, 03/2004
APECS (cont.)
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APECS uses ACS to provide the necessary
infrastructure to observe with APEX:
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Observer CLI & GUI to set up scans for a
number of standard observing modes
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Telescope control (via TICS) & device setup
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Raw data (MBFITS) writing
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Online calibration (TA*) and data reduction for
pointing, focus and skydip
ACS Workshop, ESO Garching, 03/2004
APECS Class Diagram
ACS Workshop, ESO Garching, 03/2004
APECS
Deployment
Diagram
ACS Workshop, ESO Garching, 03/2004
ACS Pros
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Hides many CORBA details
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Allows for flexible distributed systems
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Simple deployment reconfiguration
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Component property model is very useful
for hardware device implementations
Remote monitoring and remote observing
is easily implemented
ACS Workshop, ESO Garching, 03/2004
ACS Cons
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Steep learning curve; lab staff typically
does not want to deal with it directly
ACS is pretty large; this conflicts with
using it in embedded systems
TCP connections get stuck when parts of
the software need to be restarted
Missing connection to existing lab tools
such as LabView
ACS Workshop, ESO Garching, 03/2004
APEX's ACS Wishlist
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Auto-reconnection does not always work
but is essential for operations
Rather get a stable and debugged ACS
than new features since ACS is the
infrastructure for everything else
Share IDL and naming structure with
other projects to facilitate re-using code
ACS Workshop, ESO Garching, 03/2004